In order to improve the low ductility of nanostructured materials,a layered and nanostructured (LN) 304 SS (stainless steel)is prepared from warm co-rolled 304 SS pre-treated by surface mechanical attrition treatment.The microstructure and mechanical properties,as well as strain hardening,are analyzed in details.The LN steels exhibit both high strength and large ductility resulting from good strain hardening behaviors.The strain hardening can be subdivided into two stages,which involves a multiple cracking along interlaminar at the first stage and a strain-induced martensite(SIM)transformation at the second stage.The SIM transformation of nanocrystallines and ultrafine grains induces a larger work hardening exponent by the formation of nanoscaled martensite phase.The effect of grain size on the transformation dynamics is discussed.
